Field of the Invention
The present invention relates to an electro-hydraulic brake system and a method for controlling the same, and more particularly, to an electro-hydraulic brake system which generates sufficient braking force to secure safety even when a pump for generating a hydraulic pressure necessary to generate braking force is out of order, and a method for controlling the same.
Description of Related Art
Recently, a vehicle brake apparatus has employed a brake-by-wire technique by which, instead of a general hydraulic pressure control system, an electronic control system is applied thereto for control.
Such an electronic control brake apparatus generates the required hydraulic pressure by using an electric motor according to driver braking intention and transfers the hydraulic pressure generated by driving the motor to each wheel brake (wheel cylinder) to generate the braking force.
The electronic control brake apparatus, which controls the hydraulic pressure by using an electronic actuator, is generally called an electro-hydraulic brake system (EHB).
The electro-hydraulic brake system can easily and individually control the brake force generated from each wheel, so that electronic stability control (ESC) or an anti-lock brake system (ABS) is easily implemented.
According to a conventional electro-hydraulic brake system, as the electric actuator described above, a pump has been widely used, in which a piston is reciprocated by converting torque into linear force when a motor is driven and presses the brake oil in a chamber of a cylinder to generate a hydraulic pressure.
In addition, after sensing a pedal stroke caused by a driver pedal operation through a sensor, the electro-hydraulic brake system controls the braking force of each wheel with the hydraulic pressure generated by the operations of the motor and the pump.
In addition, the electro-hydraulic brake system includes a pedal simulator for allowing a driver to feel a pedal pressure like a general hydraulic brake apparatus.
Thus, when a driver steps on a pedal connected to a backup master cylinder to press the pedal, the hydraulic pressure of the brake oil inside the backup master cylinder is increased and the hydraulic pressure of the backup master cylinder is transferred to the pedal simulator through a pedal hydraulic line to generate pedal feel.
In addition, when a driver steps on a brake pedal, a controller calculates a driver desired target hydraulic pressure based on a driver pedal input value (brake input value), that is, a pedal stroke value, sensed through a brake pedal sensor (pedal stroke sensor), and controls the operation of a motor to allow the pump to generate a hydraulic pressure according to the calculated target hydraulic pressure. Then, the hydraulic pressure generated from the pump is transferred to each wheel cylinder to obtain the desired braking power.
However, since the electro-hydraulic brake system according to the related art generates and controls the hydraulic pressure required to generate the braking power by using only one pump driven by a motor without regard to the braking condition, the electro-hydraulic brake system requires a large size of a pump.
The pump having a large size has too heavy weight and is very expensive due to a manufacturing problem.
In addition, when a pump is failed, for example, when the motor is out of order, since the braking force is generated only by pedaling force of a driver in emergency, that is, the hydraulic pressure of the backup master cylinder, it is difficult to secure sufficient braking power so that the brake stability is deteriorated and braking distance is increased.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.